CN109406451B - Cold spring gas component and concentration detection device and detection method - Google Patents
Cold spring gas component and concentration detection device and detection method Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
Abstract
The invention belongs to the technical field of optical gas detection, and particularly relates to a cold spring gas component and concentration detection device and a detection method. The device comprises a signal generation module, a gas component analysis module, a gas concentration detection module and a control module; the signal generation module is used for generating a laser driving signal, a modulation signal and a phase-locked amplified local reference signal; the gas component analysis module is used for analyzing the gas components in the detected gas through extraction and comparison of the gas absorption peaks; the gas concentration detection module is used for inverting the gas concentration by adopting phase-locked amplification and harmonic detection according to the analysis result of the gas components; the control module is used for controlling signal generation of the signal generation module, absorption peak comparison in the gas component analysis module and phase synchronization in the gas concentration detection module. The device and the method can realize the identification of various gas components in cold spring gas and the measurement of the concentration of each gas component.
Description
Technical Field
The invention belongs to the technical field of optical gas detection, and particularly relates to a cold spring gas component and concentration detection device and a detection method.
Background
Cold spring gas is mixed gas discharged into the ocean along with sediment pore water in the form of bubbles or dissolved gas, and hydrocarbon gas such as methane, ethane and the like, and hydrogen sulfide, carbon dioxide, hydrogen and the like are used as main components.
The abnormal concentration of cold spring gas in seawater is an intuitive and effective means for defining a natural gas hydrate development area, and is also an effective way for analyzing the hydrate formation cause type and determining a hydrate mineral gas source. This is because when cold spring gas contains heavy hydrocarbon gas components, this means that conventional oil and gas resources may be present in the deep deposition of the zone. Therefore, the method has important resource development value for accurately detecting the components and the concentration of cold spring gas in the seawater.
Tunable diode laser absorption spectroscopy (Tunable Diode Laser Absorption Spectroscopy, TDLAS) technology is a gas detection method that applies laser technology to absorption spectroscopy measurements. Due to their advantages in terms of resolution, sensitivity, selectivity, etc., they have become one of the effective methods for rapid, on-line analysis of trace gases.
In practical applications of TDLAS technology, in order to improve the accuracy and sensitivity of gas detection, a high-frequency sine wave modulation technique is generally adopted at a light source, and lock-in amplification and harmonic extraction techniques are adopted at a signal receiving site. This is because, in gas detection, especially in trace gas detection, the light intensity signal received by the detector is very small compared with the large background signal, which is unfavorable for direct concentration measurement, and the introduction of the technology can effectively filter noise and background signal interference, thereby separating useful signals and finally improving signal-to-noise ratio and detection sensitivity.
In the prior art, TDLAS technology is mostly used for measuring the concentration of a single gas component, and when the measured gas contains multiple gas components, the variety of the contained gas needs to be predicted, and multiple sets of lasers and gas detection channels thereof are configured accordingly, so that the system has complex structure and poor universality. In addition, for the output signal of the gas detector, phase lock amplification is generally performed by using a phase lock loop, but feedback control of the phase lock loop has a disadvantage in weak signal detection of trace gas and a phase convergence speed is slow.
Disclosure of Invention
Aiming at the technical problems, the invention provides a cold spring gas component and concentration detection device which can realize the identification of various gas components in cold spring gas and the rapid and accurate measurement of the concentration of each gas component.
The invention is realized by the following technical scheme:
the cold spring gas component and concentration detection device is used for identifying various gas components in cold spring gas and measuring the concentration of each gas component; the system comprises a signal generation module, a gas component analysis module, a gas concentration detection module and a control module;
the signal generation module is used for generating a laser driving signal, a modulation signal and a phase-locked amplified local reference signal;
the gas component analysis module is used for analyzing the gas components in the detected gas through extraction and comparison of the gas absorption peaks;
the gas concentration detection module is used for inverting the gas concentration by adopting phase-locked amplification and harmonic detection according to the analysis result of the gas components;
and the control module is used for controlling the signal generation of the signal generation module, controlling the absorption peak comparison in the gas component analysis module and controlling the phase synchronization in the gas concentration detection module.
Further, the signal generation module generates a laser driving signal and a linear frequency modulation signal for gas component analysis; the frequency of the laser driving signal is f d Is a sawtooth wave; the frequency band of the linear frequency modulation signal is f LFM ∈(f L ,f H ) Is a sine wave, and f L >>f d 。
Further, the gas component analysis module comprises a gas absorption peak extractor and a typical absorption peak sample library; after the absorption peak information of the detected gas is extracted by the gas absorption peak extractor, comparing the information with typical gas absorption peaks in the typical absorption peak sample library to obtain various gas components in the detected gas;
the control module records the absorption peak information in the detected gas and feeds back the information to the signal generating module for fixed frequency modulation signal,the method comprises the following steps: the control module controls the signal generation module to sequentially generate fixed-frequency modulation signals taking the frequency band of the detected gas absorption peak as the fundamental frequency according to the frequency band of the detected gas absorption peak, and the signal generation module generates a frequency f for phase-locked amplification r Is used for the local reference signal of the mobile terminal.
Further, the fixed frequency modulation signal and the local reference signal are used for detecting the concentration of each gas component in the detected gas;
the fixed frequency modulation signal and the local reference signal adopt the same reference clock;
the fixed frequency modulation signal is a sine wave, and the local reference signal is a sine wave or a square wave.
Further, the gas concentration detection module comprises a gas absorption chamber, a gas attenuation chamber and a photoelectric detector respectively connected with the gas absorption chamber and the gas attenuation chamber;
the fixed frequency modulation signal and the laser driving signal modulate a laser, a detection light beam formed by the laser enters the gas absorption chamber and the gas attenuation chamber respectively in two paths, the detection light beam is fully absorbed and then is received by the photoelectric detector, an output signal of the photoelectric detector is used as a phase-locked amplified detected signal, a local reference signal generated by the signal generation module is used as a phase-locked amplified local signal, and second harmonic extraction is performed through a multiplier and low-pass filtering, so that detected gas concentration information is obtained.
Further, the signal output by the photodetector includes two paths: the first path of output signal det1 is directly output to the multiplier, and the second path of output signal det2 is output to the multiplier after band-pass filtering;
the local reference signal comprises two paths: the first path of local reference signal ref1 is output to the multiplier through the phase shifter I, and the second path of local reference signal ref2 is sequentially output to the multiplier through the phase shifter I, the frequency multiplier and the phase shifter II;
pairing the first path of output signal det1 with the first path of local reference signal ref1, and obtaining a final phase value phi of the phase shifter I by the control module according to the optimal direct current component of low-pass output of the multiplier; then, the second output signal det2 and the second path of local reference signal ref2 are paired, a phase value phi is given to the phase shifter I, and second harmonic detection of the output signal of the photoelectric detector is carried out; wherein the local reference signal and the fixed frequency modulation signal are co-frequency.
Further, the signal output by the photodetector includes two paths: the first path of output signal det1 is directly output to the multiplier, and the second path of output signal det2 is output to the multiplier after band-pass filtering;
the local reference signal comprises two paths: the first path of local reference signal ref1 is output by the phase shifter I, is input to the multiplier after being output by the frequency divider, and the second path of local reference signal ref2 is output to the multiplier after being sequentially output by the phase shifter I and the phase shifter II;
pairing the first path of output signal det1 with the first path of local reference signal ref1, and obtaining a final phase value phi of the phase shifter I by the control module according to the optimal direct current component of low-pass output of the multiplier; then, the second output signal det2 and the second path of local reference signal ref2 are paired, a phase value phi is given to the phase shifter I, and second harmonic detection of the output signal of the photoelectric detector is carried out; wherein the frequency of the local reference signal is 2 times of the frequency of the single-frequency modulation signal.
Further, two paths of signals output by the photoelectric detector and two paths of local reference signals are selected by the control module;
the acquisition and recording of the final phase value phi of the phase shifter I is performed by the control module.
Further, the phase adjustment range of the phase shifter I is 0-pi, and the phase adjustment range of the phase shifter II is pi/2.
The cold spring gas component and concentration detection method adopts the cold spring gas component and concentration detection device, and comprises a gas component detection step and a gas concentration detection step;
the gas component detection step includes:
the signal generating module generates a laser driving signalS1 and a linear frequency modulation signal S2; the laser driving signal S1 is used for driving and adjusting the laser with the frequency f d Is a sawtooth wave; the linear frequency modulation signal is sine wave, and the frequency range is f LFM ∈(f L ,f H ) And f L >>f d ；
The detection light generated by the laser modulated by the laser driving signal S1 enters a gas absorption chamber, the absorption peak information of the detected gas is extracted by a gas absorption peak extractor in the gas component analysis module based on the optical absorption characteristics of the gases with different components in different frequency bands, and then the absorption peak information is compared with the typical gas absorption in the typical absorption peak sample library, so that the gas components in the detected gas can be obtained;
the control module is used for recording absorption peak information in the detected gas;
the gas concentration detection step includes:
the control module controls the signal generation module to sequentially generate a fixed frequency modulation signal S3 taking the frequency band of the detected gas absorption peak as a fundamental frequency and a frequency f for phase-locked amplification according to the frequency band of the detected gas absorption peak r Is a local reference signal S4; the frequency of the fixed frequency modulation signal S3 is f m ，f r ＝f m ；
The fixed frequency modulation signal S3 and the laser driving signal S1 modulate a laser, and a detection light beam formed by the laser enters the gas absorption chamber and the gas attenuation chamber respectively in two paths, and is subjected to signal receiving by the photoelectric detector after being fully absorbed;
the photoelectric detector outputs two paths of signals: the first path of output signal det1 is directly output to the multiplier, and the second path of output signal det2 is output to the multiplier after band-pass filtering;
the local reference signal S4 includes: the first path of local reference signal ref1 is output to the multiplier through the phase shifter I, and the second path of local reference signal ref2 is sequentially output to the multiplier through the phase shifter I, the frequency multiplier and the phase shifter II;
pairing the first path of output signal det1 with the first path of local reference signal ref1, and obtaining a final phase value phi of the phase shifter I by the control module according to the optimal direct current component of low-pass output of the multiplier; and then the second output signal det2 and the second path of local reference signal ref2 are paired, a phase value phi is given to the phase shifter I, and the second harmonic detection of the output signal of the photoelectric detector is carried out.
The device disclosed by the invention is adopted to cooperatively cooperate with each module in the cold spring gas component and concentration detection process. In the aspect of gas component analysis, the control module controls the signal generation module to generate a laser driving signal S1 and a linear frequency modulation signal S2, and the driving gas component analysis module analyzes the gas components in the gas to be detected to obtain and record a gas component analysis result; in the aspect of gas concentration detection, the control module controls the signal generation module to generate a driving signal S1, a fixed-frequency modulation signal S3 and a local reference signal S4 according to the analysis result of the gas components, and the gas concentration detection module is driven to detect the concentration of each gas component. In addition, when the gas concentration is detected, the control module adjusts the phase shifter I to obtain and record the phase locking phase phi, and finally, the concentration detection of each gas component is realized.
The beneficial technical effects of the invention are as follows:
1) The device obtains the gas component information according to the typical absorption peaks of different frequency bands by modulating the wavelength of the tunable laser, and improves the detection precision and efficiency of the gas concentration by an improved phase-locked amplification technology.
2) In practical application, because the amplitude of the second harmonic is proportional to the gas concentration, for low-concentration gas, on one hand, the lower optical absorption of the gas can lead the amplitude of the second harmonic to approach zero, thereby leading to no effective input of the phase-locked loop and leading to the failure of the phase-locked loop; on the other hand, jitter of the local reference signal may introduce errors in the phase synchronization process. In the phase-locked amplifying process, the device and the method of the invention firstly carry out phase synchronization through the first harmonic wave, and then carry out second harmonic wave detection according to the obtained synchronous phase, and the step-by-step processing mode of phase synchronization and gas detection can improve the accuracy and the reliability of synchronous phase acquisition by utilizing stronger first harmonic wave on one hand, and can shorten the detection time of the second harmonic wave and reduce the detection error introduced by jitter of a reference signal on the other hand. Therefore, the phase-locked phase can be obtained more accurately and reliably by the phase-locked amplification processing method, the influence of the reference signal error on gas detection is reduced, and the sensitivity and the accuracy of gas detection are further improved.
Drawings
FIG. 1 is a schematic diagram showing the components and concentration of a gas in a rapid detection apparatus according to embodiment 1 of the present invention;
FIG. 2 is a schematic diagram showing the composition of a rapid gas component and concentration detection apparatus according to example 1 of the present invention;
FIG. 3 is a schematic diagram showing the generation of local reference signals for a rapid gas component and concentration detection apparatus according to embodiment 2 of the present invention;
FIG. 4 is a flow chart of a method for rapid detection of gas composition and concentration in an embodiment of the invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
On the contrary, the invention is intended to cover any alternatives, modifications, equivalents, and variations as may be included within the spirit and scope of the invention as defined by the appended claims. Further, in the following detailed description of the present invention, certain specific details are set forth in order to provide a better understanding of the present invention. The present invention will be fully understood by those skilled in the art without the details described herein.
Aiming at the technical problems that in the prior art, the TDLAS technology is mostly used for measuring the concentration of a single gas component, when the detected gas contains a plurality of gas components, the types of the contained gas are usually required to be predicted, a plurality of sets of lasers and gas detection channels thereof are configured according to the types of the contained gas, and the system is complex in structure and poor in universality; in addition, the phase-locked loop is generally adopted to amplify the output signal of the gas detector in the prior art, but the feedback control of the phase-locked loop has the technical problems of insufficient detection of the weak signal of trace gas and slower phase convergence speed. The invention provides the following examples:
example 1
The cold spring gas component and concentration detection device is used for identifying various gas components in cold spring gas and measuring the concentration of each gas component; as shown in fig. 1 and 2, the system comprises a signal generation module, a gas component analysis module, a gas concentration detection module and a control module;
the signal generation module is used for generating a laser driving signal, a modulation signal and a phase-locked amplified local reference signal; preferably, in an embodiment, the signal generating module selects the signal generator 101.
The gas component analysis module is used for analyzing the gas components in the detected gas through extraction and comparison of the gas absorption peaks;
the gas concentration detection module is used for inverting the gas concentration by adopting phase-locked amplification and harmonic detection according to the analysis result of the gas components;
and the control module is used for controlling the signal generation of the signal generation module, the absorption peak comparison in the gas component analysis module and the phase synchronization in the gas concentration detection module. Preferably, in an embodiment, the signal generating module uses a controller 106.
In this embodiment, the signal generator 101 is connected to a signal input end of the laser 102, a signal output end of the laser 102 is connected to the gas absorption chamber 103 and the gas attenuation chamber 107, and the gas absorption chamber 103 is connected to the absorption peak extractor 104 and the absorption peak sample chamber 105 in sequence; the absorption peak extractor 104 is connected with the controller 106; the controller 106 is connected with the signal generator 101;
the gas absorption chamber 103 and the gas attenuation chamber 107 are respectively connected with the photoelectric detector I and the photoelectric detector II, the signal output ends of the photoelectric detector I and the photoelectric detector II are divided into two paths, one path is connected with the multiplier port 1, and the other path is connected with the multiplier port 2 through the band-pass filter 110;
the phase shifter I111 of the signal generator 101 is connected, the output end of the phase shifter I111 is divided into two paths, and one path is connected with the multiplier port 4; the other path is connected with the multiplier port 3 after passing through the frequency multiplier 112 and the phase shifter II 113.
The signal generator 101 generates a laser driving signal S1 and a chirp modulated signal S2, the laser driving signal S1 and the chirp modulated signal S2 being used to drive and adjust the laser 102; wherein the laser driving signal has a frequency f d The linear frequency modulation signal is a sawtooth wave with a frequency band f LFM ∈(f L ,f H ) And f is a sine wave of L Far above f d . In the present embodiment, f d The frequency range of the frequency is 20-50 Hz, f L The frequency range of the frequency is 20-50 kHz.
The gas composition analysis module includes a gas absorption peak extractor 104 and a representative absorption peak sample library 105; the absorption peak information of the detected gas is extracted by the gas absorption peak extractor 104 in the gas component analysis module and then is compared with the typical gas absorption in the typical absorption peak sample library 105, so that the gas component in the detected gas can be obtained;
the controller 106 sequentially generates a fixed frequency modulation signal S3 with the frequency band of the detected gas absorption peak as the fundamental frequency and a frequency f for phase-locked amplification by the control signal generator 101 according to the frequency band of the detected gas absorption peak r Is a local reference signal S4; the frequency of the fixed frequency modulation signal S3 is f m ，f r ＝f m ；
The fixed frequency modulation signal S3 and the local reference signal S4 are used for detecting the concentration of each gas component in the detected gas; the fixed frequency modulation signal S3 and the local reference signal S4 adopt the same reference clock; the fixed frequency modulation signal S3 is a sine wave, the local reference signal S4 is a sine wave or a square wave, and the fixed frequency modulation signal and the local reference signal are the same frequency.
The gas concentration detection module comprises a gas absorption chamber 103, a gas attenuation chamber 107 and photoelectric detectors (comprising a photoelectric detector I and a photoelectric detector II) which are respectively connected with the gas absorption chamber and the gas attenuation chamber;
the fixed frequency modulation signal S3 and the laser driving signal S1 modulate the wavelength of the laser, the detection beam formed by the laser enters the gas absorption chamber 103 and the gas attenuation chamber 107 respectively in two paths, after being fully absorbed, the detection beam is received by the photoelectric detector (including the photoelectric detector i and the photoelectric detector ii), the output signal of the photoelectric detector is used as a detected signal of phase-locked amplification, the local reference signal generated by the signal generating module is used as a local signal of phase-locked amplification, and the second harmonic extraction is performed through a multiplier and low-pass filtering, so as to obtain the concentration information of the detected gas.
In order to improve the phase synchronization efficiency of phase-locked amplification, first harmonic is adopted for phase matching, and second harmonic detection is carried out based on the first harmonic. The specific method comprises the following steps:
the signal output by the photoelectric detector comprises two paths: the first path of output signal det1 is directly output to the multiplier, and the second path of output signal det2 is output to the multiplier after band-pass filtering;
the local reference signal comprises two paths: the first path of local reference signal ref1 is output to the multiplier through the phase shifter I, and the second path of local reference signal ref2 is sequentially output to the multiplier through the phase shifter I, the frequency multiplier and the phase shifter II;
the first path of output signal det1 is sent to a multiplier 114 through a multiplier port 1, the first path of local reference signal ref1 is sent to the multiplier 114 through a phase shifter I111 (the phase modulation range is 0-pi) through a multiplier port 4, the output of the multiplier 114 is filtered 115 to obtain a direct current component, the controller 106 obtains the optimal direct current output by adjusting the phase value of the phase shifter I, and the phase value phi at the moment is recorded as the adjustment phase of the phase shifter I (namely the final phase value phi of the phase shifter I); the second output signal det2 is then bandpass filtered 110 (2 f m ) Extracting the second harmonic and sending the second harmonic to a multiplier through a multiplier port 2The second local reference signal ref2 is added with a phase phi through a phase shifter I, then is sent into a multiplier through a frequency multiplier (double frequency) 112 and a phase shifter II113 (phase shift pi/2) through a multiplier port 3, and at the moment, the output of the multiplier is subjected to low-pass filtering to obtain gas concentration information.
In this embodiment, the selection of the photodetector output signals det1 and det2 and the two local reference signals ref1 and ref2 is performed by the control module.
In this embodiment, the acquisition and recording of the final phase value phi of the phase shifter I is performed by the control module.
Example 2
Embodiment 2 is basically the same as embodiment 1, except that as shown in fig. 3, the present embodiment provides another generation method of the local reference signal S4. To facilitate detection of the second harmonic of the detection signal, the signal generator 101 generates a local reference signal S4, i.e. f, having a frequency 2 times the frequency of the fixed frequency modulation signal S3 r ＝2f m . The local reference signal is divided into two paths, one path is sent to the multiplier port 3 through the phase shifters I (0-pi) and II (pi/2) for second harmonic detection, and the other path is sent to the multiplier port 4 through the frequency divider 116 for obtaining the phase value of the corresponding phase shifter I when the optimal direct current output is obtained.
The rapid detection device for the gas components and the concentration of the embodiment can realize the detection function of various gas components through a relatively simple system structure, and has strong practicability; and through improved phase-locked amplification and harmonic detection technology, the concentration values of various gases can be obtained rapidly and accurately, and the method is suitable for rapid and accurate analysis and detection of mixed gases.
Example 3
The embodiment of the invention provides a cold spring gas component and concentration detection method, which adopts the cold spring gas component and concentration detection device described in the embodiment 1, and comprises a gas component detection step and a gas concentration detection step, as shown in fig. 4;
the gas component detection step includes:
the signal generator 101 generates a driving signal S1 and a chirp modulated signalS2 is used to drive and adjust the laser 102, wherein the drive signal S1 is a sawtooth signal with a frequency f d The chirp modulated signal S2 is a sinusoidal signal with a frequency range f LFM ∈(f L ,f H ) And f L Far above f d . In the present embodiment, f d The frequency range of the frequency is 20-50 Hz, f L The frequency range of the frequency is 20-50 kHz. The probe light generated by the modulated laser enters the gas absorption chamber 103, and the gas components in the detected gas can be obtained by comparing the absorption peak extractor 104 with the typical gas absorption in the absorption peak sample library 105 because the gases with different components have optical absorption characteristics in different frequency bands. Meanwhile, the controller 106 will record the absorption peak information in the measured gas.
The gas concentration detection step includes:
based on the gas component obtained by the frequency-modulated light beam and the frequency band where the absorption peak is located, the controller 106 controls the signal generator 101 to sequentially generate a fixed-frequency modulation signal S3 with the frequency band where the absorption peak is located as the fundamental frequency, and the frequency of the fixed-frequency modulation signal S3 is f m The frequency corresponding to the constant frequency modulation signal S3 corresponding to the ith gas component in the measured gas is f m ＝f ai I is the number of gas component sequences in the detected gas, i is more than or equal to 0 and less than or equal to N, and N is the total number of the gas species in the detected gas;
the following concentration measurements were performed for each gas component in the measured gas:
the laser 102 is modulated with the constant frequency modulation signal S3i corresponding to the i-th gas component together with the drive signal S1, and concentration detection of each gas component is started in sequence. The detection beam formed by the laser enters the gas absorption chamber 103 and the gas attenuation chamber 107 respectively in two paths, and is subjected to signal receiving by the photodetectors (108 and 109) after being fully absorbed. The purpose of differential detection in two paths is to improve the accuracy of gas concentration detection. The second harmonic of the output signal of the photodetector carries the gas concentration information, and the gas concentration is inverted by harmonic detection of the output signal in a phase-locked amplification mode.
Phase lockThe amplified detected signal is the output signal of the photodetector, the local reference signal S4i corresponding to the ith gas component is generated by the signal generator 101, the frequency is the same as the constant frequency modulation signal S3, i.e. f r ＝f m The waveform is a sine wave. In order to improve the phase synchronization efficiency of the lock-in amplification, the first harmonic is used for phase matching, and the second harmonic is detected based on the first harmonic. The specific method comprises the following steps: firstly, a photoelectric detector output signal is sent to a multiplier 114 through a multiplier port 1 and a local reference signal is sent to a multiplier port 4 through a phase shifter I111 (phase modulation range 0-pi), a direct current component is obtained through low-pass filtering 115 after the output of the multiplier, a controller 106 obtains an optimal direct current output by adjusting a phase value of the phase shifter I, and the phase value phi at the moment is recorded as an adjusting phase of the phase shifter I; next, the output signal of the photodetector is bandpass filtered 110 (2 f m ) Extracting second harmonic wave, sending the second harmonic wave into a multiplier through a multiplier port 2, adding a phase phi into a local reference signal through a phase shifter I, sending the phase phi into the multiplier through a frequency multiplier (double frequency) 112 and a phase shifter II (phase shift pi/2) through a multiplier port 3, and obtaining the gas concentration ci corresponding to the ith gas component through low-pass filtering of the output of the multiplier.
The above steps are repeated until the concentration of each gas component in the measured gas is measured.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (5)
1. The cold spring gas component and concentration detection device is characterized by being used for identifying various gas components in cold spring gas and measuring the concentration of each gas component; the system comprises a signal generation module, a gas component analysis module, a gas concentration detection module and a control module;
the signal generation module is used for generating a laser driving signal, a modulation signal and a phase-locked amplified local reference signal;
the gas component analysis module is used for analyzing the gas components in the detected gas through extraction and comparison of the gas absorption peaks;
the gas concentration detection module is used for inverting the gas concentration by adopting phase-locked amplification and harmonic detection according to the analysis result of the gas components;
the control module is used for controlling the signal generation of the signal generation module, controlling the absorption peak comparison in the gas component analysis module and controlling the phase synchronization in the gas concentration detection module;
the signal generation module generates a laser driving signal and a linear frequency modulation signal for gas component analysis; the frequency of the laser driving signal is f d Is a sawtooth wave; the frequency band of the linear frequency modulation signal is f LFM ∈(f L ,f H ) Is a sine wave, and f L >>f d ；
The gas component analysis module comprises a gas absorption peak extractor and a typical absorption peak sample library; after the absorption peak information of the detected gas is extracted by the gas absorption peak extractor, comparing the information with typical gas absorption peaks in the typical absorption peak sample library to obtain various gas components in the detected gas;
the control module records absorption peak information in the detected gas and feeds back the information to the signal generation module for fixed frequency modulation signals, and the method specifically comprises the following steps: the control module controls the signal generation module to sequentially generate fixed-frequency modulation signals taking the frequency band of the detected gas absorption peak as the fundamental frequency according to the frequency band of the detected gas absorption peak, and the signal generation module generates a frequency f for phase-locked amplification r Is a local reference signal of (a);
the fixed frequency modulation signal and the local reference signal are used for detecting the concentration of each gas component in the detected gas;
the fixed frequency modulation signal and the local reference signal adopt the same reference clock;
the fixed frequency modulation signal is a sine wave, and the local reference signal is a sine wave or a square wave;
the gas concentration detection module comprises a gas absorption chamber, a gas attenuation chamber and a photoelectric detector which is respectively connected with the gas absorption chamber and the gas attenuation chamber;
the fixed frequency modulation signal and the laser driving signal modulate a laser, a detection light beam formed by the laser enters the gas absorption chamber and the gas attenuation chamber respectively in two paths, the detection light beam is fully absorbed and then is received by the photoelectric detector, an output signal of the photoelectric detector is used as a phase-locked amplified detected signal, a local reference signal generated by the signal generating module is used as a phase-locked amplified local signal, and second harmonic extraction is carried out through a multiplier and low-pass filtering, so that detected gas concentration information is obtained;
the signal output by the photoelectric detector comprises two paths: the first path of output signal det1 is directly output to the multiplier, and the second path of output signal det2 is output to the multiplier after band-pass filtering;
the local reference signal comprises two paths: the first path of local reference signal ref1 is output to the multiplier through the phase shifter I, and the second path of local reference signal ref2 is sequentially output to the multiplier through the phase shifter I, the frequency multiplier and the phase shifter II;
pairing the first path of output signal det1 with the first path of local reference signal ref1, and obtaining a final phase value phi of the phase shifter I by the control module according to the optimal direct current component of low-pass output of the multiplier; then, the second output signal det2 and the second path of local reference signal ref2 are paired, a phase value phi is given to the phase shifter I, and second harmonic detection of the output signal of the photoelectric detector is carried out; wherein the local reference signal and the fixed frequency modulation signal are co-frequency.
2. The cold spring gas composition and concentration detection apparatus according to claim 1, wherein the signal output by the photodetector comprises two paths: the first path of output signal det1 is directly output to the multiplier, and the second path of output signal det2 is output to the multiplier after band-pass filtering;
the local reference signal comprises two paths: the first path of local reference signal ref1 is output by the phase shifter I, is input to the multiplier after being output by the frequency divider, and the second path of local reference signal ref2 is output to the multiplier after being sequentially output by the phase shifter I and the phase shifter II;
pairing the first path of output signal det1 with the first path of local reference signal ref1, and obtaining a final phase value phi of the phase shifter I by the control module according to the optimal direct current component output by the low-pass of the multiplier, and completing phase synchronization through first harmonic; then, the second output signal det2 and the second path of local reference signal ref2 are paired, a phase value phi is given to the phase shifter I, and second harmonic detection of the output signal of the photoelectric detector is carried out; wherein the frequency of the local reference signal is 2 times of the frequency of the single-frequency modulation signal.
3. The cold spring gas composition and concentration detection apparatus according to claim 2, wherein the selection of two signals output by the photodetector and two of the local reference signals is performed by the control module;
the acquisition and recording of the final phase value phi of the phase shifter I is performed by the control module.
4. The cold spring gas component and concentration detection apparatus according to claim 2, wherein the phase adjustment range of the phase shifter I is 0 to pi, and the phase adjustment of the phase shifter II is pi/2.
5. A cold spring gas composition and concentration detection method, adopting a cold spring gas composition and concentration detection device according to any one of claims 1-4, characterized in that the method comprises a gas composition detection step and a gas concentration detection step;
the gas component detection step includes:
the signal generation module generates a laser driving signal S1 and a linear frequency modulation signal S2; the laser driving signal S1 is used for driving and adjusting the laser with the frequency f d Is a sawtooth wave; the linear frequency modulation signal is sine wave, and the frequency range is f LFM ∈(f L ,f H ) And f L >>f d ；
The detection light generated by the laser modulated by the laser driving signal S1 enters a gas absorption chamber, the absorption peak information of the detected gas is extracted by a gas absorption peak extractor in the gas component analysis module based on the optical absorption characteristics of the gases with different components in different frequency bands, and then the absorption peak information is compared with the typical gas absorption in a typical absorption peak sample library, so that the gas components in the detected gas can be obtained;
the control module is used for recording absorption peak information in the detected gas;
the gas concentration detection step includes:
the control module controls the signal generation module to sequentially generate a fixed frequency modulation signal S3 taking the frequency band of the detected gas absorption peak as a fundamental frequency and a frequency f for phase-locked amplification according to the frequency band of the detected gas absorption peak r Is a local reference signal S4; the frequency of the fixed frequency modulation signal S3 is f m ，f r ＝f m ；
The fixed frequency modulation signal S3 and the laser driving signal S1 modulate a laser, and a detection light beam formed by the laser enters the gas absorption chamber and the gas attenuation chamber respectively in two paths, and is subjected to signal receiving by a photoelectric detector after being fully absorbed;
the photoelectric detector outputs two paths of signals: the first path of output signal det1 is directly output to the multiplier, and the second path of output signal det2 is output to the multiplier after band-pass filtering;
the local reference signal S4 includes: the first path of local reference signal ref1 is output to the multiplier through the phase shifter I, and the second path of local reference signal ref2 is sequentially output to the multiplier through the phase shifter I, the frequency multiplier and the phase shifter II;
pairing the first path of output signal det1 with the first path of local reference signal ref1, and obtaining a final phase value phi of the phase shifter I by the control module according to the optimal direct current component output by the low-pass of the multiplier, and completing phase synchronization through first harmonic; and then the second output signal det2 and the second path of local reference signal ref2 are paired, a phase value phi is given to the phase shifter I, and the second harmonic detection of the output signal of the photoelectric detector is carried out.
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